One of the most common questions I get is when I suggest insulating an unvented attic space.

“Doesn’t that cause the shingles to overheat and fail prematurely?”

I’m not sure where this question comes from other than perhaps some roofing companies and contractors have made some noise recently about how shingles if they cannot vent some heat downward into the attic, may fail prematurely.

Is this true? Does the temperature of a shingle get so high that it might fail by warping, melting, or splitting?

Let’s look at some facts.

A Study Out of Florida is Interesting

Someone at the Florida Solar Energy Center (FSEC) went through the time and trouble to research this very claim.

During the summer of 2000, they measured the temperature of shingles for houses that had insulation at the flat ceiling level with a vented attic, and shingle temperatures for houses that had insulation along the roofline.

(You can see the graphs and download the study here)

Take a look at figure 11. This graph clearly shows that the temperature difference between these two roofs is pretty much the same over 15 minutes.

Yes, I know, what about the rest of the day, you are asking. Don’t worry, you can find that info in the next graph, entitled Figure 12.

There is only about a 9-degree difference which happens at about noon, as you might expect. During the remainder of the day, there is only a 2- degree Fahrenheit difference.

It’s doubtful that anyone would notice a 2-degree difference in room temperature, so why do they believe that the shingles on your roof would sustain damage?

Is That 9 Degrees Enough to Make a Shingle Fail?

While it’s true that 9 degrees will make all the difference between really hot water and boiling water, this isn’t the case with roofing shingles.

This study did not take shingle failure into account. A study would need to last 20 years or longer to determine if 9 degrees would hurt a shingle since most roofs are guaranteed to last for 15-30 years.

However, when you consider that roofing shingles often run about 150 degrees, it doesn’t appear that 9 degrees is going to make that much of a difference.

How do I know?

Don’t take my word for it, take a look at Southface. Southface is a non-profit that has been building houses for decades.

They have insulated panels that they built back in 1996. This means that the asphalt shingles have been on an insulated roofline for 26 years. There is also a detached garage with a vented attic.

There is zero difference either in the performance or the appearance of the roofing shingles.

Also, during my many decades of service, I have never seen shingles fail due to excessive heat buildup in the attic.

A Question for Chicagoans

Have you ever met anyone, anywhere, whoever collected on a shingle warranty?

I’m betting your answer is no. I know that I am certainly unaware of even one person ever collecting on a warranty for their roof shingles.

Even if someone did manage to collect on a shingle warranty, since these are prorated, they didn’t collect much unless they had some catastrophic disaster happen in the first two or three years.

Roofing manufacturers make these warranties difficult to collect because they know all the hoops you will have to jump through usually are not worth the trouble.

Saying that an unvented attic with spray foam insulation may cause premature failure of the shingles is just one more loophole roofing manufacturers are using to prevent you from ever collecting on the warranty.